A closure for a multiple component container includes an insert (12), a piston (20) and a cap (10). The insert (12) and the piston (20) define a reservoir and the insert (12) comprises a fixed cylindrical wall (26) and a movable wall (32) connected thereto and movable with respect thereto by the action of gas pressure within the reservoir. The movable wall (32) has a discharge aperture (36) formed therein. The cap (10) comprises a closure plate (14), integral with whose outer edge is a depending skirt (16), by means of which the cap may be secured to a container. The closure plate (14) cooperates with the piston (20) such that movement of the closure plate towards the insert (12) results in movement of the piston also in the same direction. The piston (20) forms a sliding seal with the internal surface of the fixed cylindrical wall (26). A valve member (22) is integral with, the piston (20) and is slidably received in and seals the discharge aperture (36).